Ground Fault Current Calculator Formula
Understand the math behind the ground fault current calculator. Each variable explained with a worked example.
Formulas Used
Ground Fault Current
ground_fault_current = system_voltage / (ground_path_impedance + source_impedance)Fault Power
fault_power = pow(system_voltage, 2) / (ground_path_impedance + source_impedance)Touch Voltage (at fault)
touch_voltage = system_voltage * ground_path_impedance / (ground_path_impedance + source_impedance)Variables
| Variable | Description | Default |
|---|---|---|
system_voltage | System Voltage (Phase-to-Ground)(V) | 277 |
ground_path_impedance | Ground Path Impedance(Ω) | 0.5 |
source_impedance | Source Impedance(Ω) | 0.1 |
How It Works
Ground Fault Current Estimation
Ground fault current flows when a live conductor contacts grounded metal. Its magnitude determines how quickly protection devices clear the fault.
Formula
I_gf = V_phase / (Z_ground + Z_source)
Touch Voltage = V_phase x Z_ground / (Z_ground + Z_source)
Low ground-path impedance ensures high fault current, which trips protective devices quickly. High impedance (poor grounding) results in low fault current that may not trip the breaker, leaving a dangerous condition.
Worked Example
277 V phase-to-ground, 0.5 ohm ground path, 0.1 ohm source impedance.
- 01Ground fault current: 277 / (0.5 + 0.1) = 461.7 A
- 02Fault power: 277^2 / 0.6 = 127,882 W
- 03Touch voltage: 277 x 0.5 / 0.6 = 230.8 V (dangerous)
Frequently Asked Questions
What is a safe touch voltage?
Below 50 V is generally safe for dry conditions (IEC 60479). Above this, ground fault protection must clear quickly (within milliseconds).
Why maintain low ground impedance?
Low impedance ensures high fault current, which trips breakers or GFCIs quickly. High impedance may prevent tripping, leaving a shock hazard.
What is GFCI/RCD protection?
Ground Fault Circuit Interrupters detect imbalance between line and neutral (indicating ground fault) and trip at 5-30 mA to protect people.
Ready to run the numbers?
Open Ground Fault Current Calculator